The oxidative dyeing of hair is one of the most extensively used methods to color hair. In this process oxidative hair coloring precursors are used in combination with an oxidizing agent, commonly a peroxy oxidizing agent. The precursors are generally small molecules capable of diffusing into hair, generally comprising primary intermediates and couplers. A wide variety of primary intermediates and couplers have been employed in such oxidative hair coloring compositions. Selections of specific combinations of couplers and primary intermediates allow reaching the desired nuance of hair color.
Besides providing the desired color, the dye precursors used for oxidative hair dyeing have to also meet some additional requirements. Indeed, the combination of couplers and primary intermediates used should deliver the desired intensity together with good wash and bleeding fastness and be acceptable from a toxicological and dermatological point of view.
Pyrazole compounds have been disclosed as oxidative dye precursors. A colorant for keratin fibers comprising a pyrazole derivative (I), a m-aminophenol derivative (II) and a pyridine derivative (III) is known. See for example EP 1166748A2.
The compositions of the prior art comprising pyrazole compounds are not satisfactory especially in terms of intensity, wash fastness and bleeding.
Furthermore, these disclosures do not disclose an example with a selection of a C6/C7 straight chain alkyl substituent on the N-1 position of a 4,5-diaminopyrazole.
The invention provides novel dye compositions that overcome known drawbacks of pyrazole compounds. In particular the invention provides good hair color intensity together with good wash and bleeding fastness. Indeed, it has surprisingly been found that the modification of the pyrazole ring system on the N-1 position by a C6/C7 straight alkyl chain combined with pyridine couplers provides excellent properties of resistance to the various treatments which keratinous fibers may undergo.